Beryllium carbonyl Be(CO) (n = 1-4) complex: a p-orbital analogy of Dewar-Chatt-Duncanson model

Transition metal-carbonyl bonds are rationalized by M ← CO σ donation and M → CO π back donation where the d orbital of the transition metal is involved. This bonding model provided by Dewar, Chatt and Duncanson (DCD) has rationalized many transition metal-ligand bonds. The involvement of p orbital in such a DCD model can be intriguing. Alkaline earth metals with ns²np⁰ configuration may appear suitable as ns⁰np² excitation has been recognized in many complexes. Herein, a theoretical study is presented for the Be(CO) (n = 1-4) complex to verify this assumption. Detailed electronic structure analyses confirmed the involvement of the p orbital of beryllium in M → CO π back donation, thereby supporting the hypothesis. EDA-NOCV results reveal that the π-back donation from the central Be atom to CO ligands significantly predominates over the σ donation from the ligands for both Be(CO)₃ and Be(CO)₄. Our calculations reveal that Be(CO)₄ is the highest carbonyl that may be experimentally detected.